Machines such as, for example, excavators, loaders, dozers, motor graders, and other types of heavy machinery use multiple hydraulic actuators to accomplish a variety of tasks. These actuators are typically velocity controlled to move a work tool at a speed based on an actuation position of an operator interface device. For example, an operator interface device such as a joystick, a pedal, or any other suitable operator interface device may be movable to a position to generate a signal corresponding to that position that is indicative of a desired velocity of an associated hydraulic actuator. When an operator moves the interface device to that specific position, the operator expects the hydraulic actuator to move at the corresponding predetermined velocity.
One example of this type of system is described in U.S. Pat. No. 5,899,008 (the '008 patent) issued to Cobo et al. on Apr. 4, 1999. The '008 patent describes an apparatus for controllably moving a work implement connected to a machine based on positional feedback. Specifically, the apparatus of the '008 patent includes an operator controlled joystick that generates an operator command signal in response to a moved position of the joystick. The signal is indicative of a desired velocity and initiates the controlled flow of hydraulic fluid to lift and tilt cylinders to move the cylinders in accordance with the desired velocity. Cylinder position sensors produce cylinder position signals in response to the position of the lift and tilt cylinders. A controller receives the operator command and cylinder position signals and responsively produces a pump command signal to change the displacement of a variable displacement pump, thereby regulating the movement speed of the hydraulic cylinders to match the desired velocity.
Although the '008 patent may provide predictable implement movement velocity, the apparatus of the '008 patent may be less responsive and less intuitive than desired by an operator of the machine. That is, there may be times when an operator desires only small movements of the lift and/or tilt cylinders, but at a high velocity. In this situation, a position only based control system may be unsatisfactory. Further, it may be more intuitive for the movement speed of the implement system to be at least partially based on the movement speed of the joystick.
The disclosed control system is directed to overcoming one or more of the problems set forth above.